The technology relates to a steering apparatus that reduces a flutter vibration, transmitted as a reverse input to a rack shaft housing.
External force containing various vibration components is applied as a reverse input to a steering system of a vehicle upon running. The reverse input is transmitted to a steering shaft through a rack shaft and a steering gear box which structure a steering apparatus, resulting in occurrence of a so-called steering vibration of the steering shaft.
A flutter vibration is a typical example of the steering vibration. The flutter vibration is a micro-vibration which is caused by an imbalance between tires and which shakes a steering wheel circumferentially in a wiggling fashion. The flutter vibration occurs notably upon high-speed running of the vehicle.
To reduce the flutter vibration, a technique is known that makes it difficult for the flutter vibration to be transmitted to a region on the steering shaft side, by applying high friction force to an axial sliding movement of the rack shaft in the steering gear box or to rotation of a pinion shaft. On the other hand, increasing the friction force in the steering gear box impairs returning of the steering wheel, which in turn necessitates a tuning work performed depending on a vehicle type and thus requires a cumbersome work.
To address the impairment, a method may be contemplated in which the returning of the steering wheel is controlled by means of an electric power steering apparatus. The method, however, may impair a feeling upon performing regular steering.
Japanese Unexamined Patent Application Publication (JP-A) No. 2005-219539 discloses a technique in which, upon detecting a frequency component attributed to the flutter vibration in high-speed running, an assist signal adapted to cancel out the frequency component is added to a motor instruction current that drives an electric power steering. Thus, the electric power steering is driven in a direction by which the flutter vibration is offset to attenuate the flutter vibration.